The present invention generally relates to intravascular catheters. More specifically, the present invention relates to intravascular catheters having braid reinforcement.
Intravascular catheters are used in a wide variety of relatively non-invasive medical procedures. Such intravascular catheters may be used for diagnostic or therapeutic purposes. Generally, an intravascular catheter allows a physician to remotely perform a medical procedure by inserting the catheter into the vascular system of the patient at a location that is easily accessible and thereafter navigating the catheter to the desired target site. By this method, virtually any target site in the patient""s vascular system may be remotely accessed, including the coronary, cerebral, and peripheral vasculature.
The distance between the access site and the target site is often in excess of 100 cm. The inside diameter of the vasculature at the access site is often less than 2 cm, and the inside diameter of the vasculature at the target site is often less than 0.5 cm. Accordingly, intravascular catheters must be relatively long and thin. Furthermore, in order to navigate through the patient""s tortuous vascular system, intravascular catheters must be very flexible. It is also desirable that intravascular catheters be relatively soft in order to minimize the probability of damaging vascular tissue.
Intravascular catheters typically have a radiopaque portion and are guided through the patient""s vascular system with the assistance of x-ray fluoroscopy. A physician may manipulate the proximal end of the catheter and fluoroscopically monitor the corresponding movement of the distal end of the catheter. It is desirable that intravascular catheters be sufficiently radiopaque along their length and particularly at their distal end such that the physician is able to clearly monitor the progress of the catheter as it is being advanced from the vascular access site to the vascular target site.
After the intravascular catheter has been navigated through the patient""s vascular system with the distal end thereof adjacent the target site, the catheter may be used for various diagnostic and/or therapeutic purposes. Frequently, diagnostic and therapeutic techniques require the infusion of fluids through the catheter. For example, it may be desirable to inject radiopaque contrast media through the catheter to provide enhanced fluoroscopic visualization for diagnostic purposes, or to inject pharmaceutical solutions (i.e., drugs) to the target site for therapeutic purposes. In order to maintain a fluid path, it is desirable that intravascular catheters be sufficiently resistant to kinking. In addition, because such fluids are delivered under pressure, it is also desirable that intravascular catheters be sufficiently resistant to bursting.
To satisfy some of these desirable features, prior art intravascular catheters have utilized a reinforcement structure such as a braid or coil disposed between an inner tubular polymer layer and an outer tubular polymer layer. A braid reinforcement structure may provide high resistance to bursting and improve the connection integrity between individual shaft segments. A coil reinforcement structure may provide adequate resistance to ovaling and kinking.
Some types of prior art intravascular catheters also utilize longitudinal or axial members to impart stiffness to the catheter shaft. For example, U.S. Pat. No. 5,057,092 to Webster discloses an intravascular catheter having a braid reinforcing mesh and longitudinal warp members. The longitudinal warp members are intended to provide increased bending stiffness and thus permit reductions in the wall thickness and/or softer materials for the inner and outer tubes. The warp members are interwoven with the braid such that warp members alternate under or over the braid mesh. Because the braid reinforcing mesh is disposed between an inner polymeric layer and an outer polymeric layer, portions of the longitudinal warp members are disposed between the braid reinforcing mesh and the adjacent polymeric layer.
With this arrangement, the adjacent polymeric layer may conform to the longitudinal warp members so as to create radial protrusions running the length of the catheter. A protrusion along the inside surface of the catheter may not be desirable because it may create friction or bias with devices inserted therein (e.g., guidewires). A protrusion along the outside surface of the catheter may not be desirable because it may create friction, bias or prevent adequate sealing with devices that the catheter is inserted into (e.g., introducer sheaths, compression fittings, etc.).
Also with this arrangement, the adjacent polymeric layer may become fixed to the longitudinal warp members as it conforms thereto. Fixing the longitudinal warp members to the adjacent polymeric layer may not be desirable because it may limit relative movement and flexure therebetween. Limiting relative movement and flexure may cause excessive stiffness in one or more planes of flexure. This may cause difficulties in manipulating and navigating the catheter through tortuous vasculature, which is clearly undesirable.
Accordingly, it is desirable to provide the advantages of a longitudinal or axial member without creating a protrusion and without fixing the axial member to the adjacent polymeric layer.
The present invention overcomes these disadvantages by providing an intravascular catheter that includes a braid reinforcement with a plurality of axial wires or fibers disposed between the helical members that form the braid. By placing the axial members between the helical members, the axial members do not create a protrusion on either side of the braid. In addition, the axial members do not become fixed to any polymer layer adjacent the braid. Thus, the present invention maintains the benefits of axial members, but without the undesirable effects of friction caused by an axial protrusion and without the undesirable effects of limited flexure caused by an adjacent polymer layer becoming fixed to the axial member.
In addition to avoiding the disadvantages discussed above by positioning the axial members between the helical members, the present invention provides several benefits by utilizing a plurality of axial members. First, the axial members prevent elongation of the shaft of the catheter thereby maintaining one-to-one correspondence in axial manipulation of the catheter, even when the shaft is placed in tension. Second, by equally spacing the axial members about the circumference of the catheter, the shaft maintains uniform flexibility in several planes of flexure thereby facilitating precise control of the catheter as it is navigated through tortuous vasculature. Third, as compared to a single axial member, uniformly spacing the axial members about the circumference of the catheter reduces the likelihood of causing the catheter to curl when the lumen of the catheter becomes clogged and the catheter is pressurized. Fourth, the strength of the connections between adjacent shaft segments is increased significantly. Fifth, the stiffness of the catheter may be uniformly increased thereby potentially reducing the profile of the catheter by allowing the wall thickness and/or hardness of the polymer layers to be reduced. Sixth, the burst strength of the catheter may be significantly increased by virtue of the axial members limiting radial expansion of the shaft.
An intravascular catheter in accordance with one embodiment of the present invention includes an elongate shaft having a lumen extending therethrough. The shaft includes an inner polymer layer, a reinforcement layer disposed about the inner layer and an outer polymer layer disposed about the reinforcement layer. The reinforcement layer comprises a tubular braid having two or more interwoven helical members. The reinforcement layer also includes a plurality of axial members disposed between the helical members such that the axial members are retained within the tubular braid structure for at least a length thereof. The axial members may be wires, fibers, filaments, cables or the like, but are generically referred to herein as axial members.
The axial members are preferably uniformly spaced about the circumference of the shaft. Virtually any number of axial members may be utilized, depending on the particular characteristics desired. For example, four or eight axial members may be utilized wherein the axial members are uniformly spaced apart by 90xc2x0 or 45xc2x0, respectively, about the circumference of the shaft. In addition, only a portion of the shaft may include a plurality of axial members. For example, the distal shaft portion may have fewer axial members than the proximal shaft portion such that the distal shaft portion is more flexible.
The helical members that form the braid may each comprise polymeric material, a metallic material, or a combination thereof. Similarly, the axial members may comprise a polymeric material or a metallic material. If a polymeric material is utilized for the helical members or the axial members, then each member may comprise a plurality of monofilaments such as LCP. The monofilaments may be held together statically thereby eliminating the need for a binding material that might otherwise add to the profile of the members. To further minimize profile, the monofilaments may be arranged side-by-side to collectively define a flat ribbon or cable.
An intravascular catheter in accordance with another embodiment of the present invention includes an elongate shaft having a reinforcement layer. The reinforcement layer comprises a tubular braid including two or more interwoven helical members and a plurality of axial members disposed between the helical members. Optionally, the catheter may include inner and/or outer polymer layers disposed on either side of the reinforcement layer. Each of the inner and/or outer layers may comprise a single layer of polymeric material or multiple layers of polymeric materials.
The present invention also provides a method of making such a catheter. The manufacturing method includes the steps of braiding two or more helical members about a plurality of axial members such that the axial members are disposed between the helical members. The axial members are preferably uniformly spaced about the circumference of the shaft. The helical members may be braided over a carrier such as a mandrel that is later removed or a polymeric tubular member that becomes the inner layer of the catheter shaft. After the reinforcement layer is woven about the carrier, another polymeric tubular member may be disposed about the reinforcement layer to become the outer layer of the catheter shaft.